Mark Webber has seen his preparations for the Malaysian Grand Prix hit by an engine issue during Friday free practice.

Webber's Red Bull ground to a halt during the second session of the day leaving the Australian to watch on from the sidelines.

However, while he admitted to being frustrated by the problem, Webber said he was still confident in the performance of the RB6 from the running he completed earlier in the day.

"It was the engine," he said. "You never want your Friday disturbed and today's problem cost us quite a bit of track time, but the car felt pretty good in the quick stuff and also at low speeds. It's never ideal to lose an engine, but we did, although it was quite high mileage.

"It's good that [Sebastian] Vettel's up there, but it's where we expected to be, it would have been nice to feel the option tyres today, but we'll have to do that tomorrow."

While Webber said he was happy with his team-mate finishing sixth in the second session, Vettel himself insisted he wasn't completely happy with how the day had gone - stating that he felt the team needed more pace against its rivals.

"I wasn't 100 per cent happy today, I think we still need to get a little bit quicker," he said. "The McLarens and the Mercedes look quick and Ferrari have a decent long run pace, so we'll have to see where we are. This circuit is one of the tougher ones here due to the hot and humid conditions."